AC and DC circuit breaking
DC circuit breakers and AC breaker main difference is the ability to arc. Because the exchange of each cycle, have had zero, zero easy to extinction in the past, but has not been zero DC switching, arc extinguishing ability is poor, so to add additional interrupter device. DC arc is generally difficult, but the exchange has zero, breaking easily. Exchange can be derived for the DC circuit breaker protection, attention to three changes: 1, overload and short circuit protection.
1. long delay overload protection.
By thermal-action (double metal components) for long delay overload protection, the source of its action as I2R, AC RMS and DC current equal to the average, there is no need to use any restructuring. However, the large current size, to the current transformer secondary current heat who can not be used due to transformer can not be used on DC circuits. Release long delay if the overload is the use of electromagnetic type (hydraulic type, that is, oil cup), then the delayed release characteristics to change, the minimum operating current to 110% -140% bigger, so the whole electromagnetic Release not be used for DC circuits (such as the use will have to re-design).
2.short circuit protection.
1.Electromagnetic type of short circuit protection and thermal dynamic electromagnetic
2.circuit breaker accessories, such as shunt release, under voltage release, electrically operated institutions; shunt, under voltage are voltage coil, as long as the line voltage, is used for systems, need not be Any change can be used for DC system. Auxiliary and alarm contacts, AC and DC common. Electric operating mechanism for the DC Time to re-design.
3. unlike the exchanges as DC current zero-crossing characteristics, dc short circuit current (or even multiple small fault current) is breaking; arc out all the difficulties, so wiring should be two extreme ways or three poles in series increase the fracture, so that the fracture energy to bear part of the arc.
• DC arcs are to be interrupted by increasing the resistance interruption method in which resistance of the arc is increased so that the arc voltage can no longer maintain the current and the arc is extinguished.
• Size of DC circuit breaker increases as the voltage level increases.
• AC arcs current reduces to zero in each cycle (2 times)
• If the circuit breaker contacts are opened at time when the current passed through zero and dielectric strength of the medium is build up rapidly so that arc cannot strike again then arc can be extinguished successfully.
• Size of AC circuit breaker can be small compared to same voltage DC circuit breaker.
